Most sponge recipes are pretty similar as its the proportion of fats/sugar/flour eggs which makes them work.Make sure you cream the fats & sugar so the mixture is really light & fluffy before you gradually add the eggs and be gentle as you fold in the flour.Also make sure the oven is up to temperature before you put the cake in, and don't open the oven door until you have to.I generally use 6oz of everything and 3 eggs, but 8 oz + 4 eggs will naturally give you a bigger cake.Another one to try is to add just the egg yolks (beaten) and then fold in the whites which you have whisked into soft peaks - all about getting air in.Don't know if this helps, but I'm sure your Mum will appreciate your efforts!

oops, when I say watch like a hawk this is through the door if you can, don't open unless you absolutely have too. If you don't have a glass door spend the last five minutes in the kitchen and as soon as you can smell cooked cake it's probably ready.

I tend to drop all the whisked whites into the bowl as the last thing that is added, and gently fold into the mixture.(when my mixture 'curdles' it never seems to make a great deal of difference to the finished cake. It's usually because I'm in a hurry and add too much egg into the mixer at once. Mum always reckoned adding flour to stop the curdling though)

I love Hugh F-W approach - he makes a yummy victoria Sponge - weigh 4 eggs in their shells. This gives the weight of SR flour, caster sugar and butter. Cream butter and sugar together untill fluffy and creamy. Add 1 egg and some flour - mix (keep going until all eggs and flour added). Put in 2 pre-lined 20cm baking trays. Cook at 180 for 25-30 minutes. When cake is cooked drop from about 30cm onto work top (stops is sinking in middle).

A 4oz, 6oz or 8oz cake serves the same number of people really. You just have much higher cakes if you increase the ingredient quantities, so the slice on your plate is higher but not wider. I always use the same cake tins.